Japanese Patent Early Publication H10-29028 discloses an apparatus having means for feeding a wire including feeding rollers from a front quill to a spring forming stage, and multiple types of radially arranged spring forming tools, which can be advanced perpendicularly or substantially perpendicularly to the axis of the wire towards the spring forming stage until they abut the wire coming out of the quill. The spring forming tools are mounted on a swivel table and can be positioned at predetermined angular positions by turning the swivel table through predetermined angles. By advancing and retreating the spring forming tools in turn on the swivel table, the tools may abut the wire, bend it, curve it, or wind it to form a spring.
In this prior art wire spring forming apparatus, the radius of a coil of a spring can be varied by adjusting the distance from the quill (wire guide) to the tools that abut the wire in the process of forming the coil. A large distance is used to form a coil of a large diameter and conversely a small distance is used to form a coil of small diameter.
However, the above-mentioned prior art apparatus has a drawback in that in adjusting the radius of the coil it is necessary to adjust the positions of the spring forming tools with respect to the quill by manipulating screws provided on the spring forming tools (Literature 1, Paragraph 0022 and FIG. 8), which is very tedious.
The prior art has another drawback in that the swivel table is provided with a set of 7 or 8 spring forming tools to attain high production efficiency. Hence, the entire swivel table, including its drive mechanism, has a considerably large moment of inertia. It is noted that the drive mechanism of each spring forming tool is set to have full advancing and receding strokes in order to prevent the mechanism from being damaged during its operation. Furthermore, each of the spring forming tools is programmed to be advanced only after the angular position of the swivel table is determined, and the swivel table is turned only after the relevant spring forming tool has finished its receding stroke. Because of the large amount of time involved in such processes and large moment of inertia of the spring forming tools, the production rate of the prior art spring forming apparatus is substantially lower than it might otherwise be. To overcome the difficulties associated with the simple advancing and retreating of spring forming tools as mentioned above, in which the wire is prevented from being scratched during the formation of a spring, it is also known to provide bending tools having a rotary body mounted on a mandrel and having projections on the periphery thereof. In order to mount this type of bending tool on the swivel table, two servomotors are provided to advance and retreat the tool and to rotate the bending tool. However, if more than one (2 say) such bending tools are mounted on the swivel table, an excessively large moment of inertia will result, so that in actuality only one bending tool can be mounted, which limits the production rate.